This invention relates to an apparatus for continuously filtering raw water.
The growth of plankton will usually bring difficulties in the supply of tap water and even of industrial water, and therefore some preventive measure is necessary. To attain this end, a variety of methods are in use, including inhibition of algae growth in a bio-ecological way, control of the propagation of plankton by chemicals, and removal of plankton by settling or by filtration. In any case, filtration must be resorted to if plankton is to be removed positively and efficiently. Among known filtration processes are slow and rapid-sand filtration, double filtration, and a process using a micro-strainer. Of these, the one that requires the least space and accomplishes filtration in the most efficient way is the last-mentioned method relying upon a micro-strainer. The method is carried into practice with an apparatus in which a fine-mesh screen of stainless steel is rolled to form a drum-shaped filter body. The body is rotatably supported by a hollow shaft. A hopper is located immovably and opposite to the rotating shaft in the upper space of the filter body. The rotating shaft is held horizontally on the water way in such a manner that the filter body is submerged in water up to about two-fifths of its height. Above the filter body, nozzles for injecting water thereinto are arranged. Altogether the components described constitute a filter equipment. In operation, the filter body is slowly rotated as raw water is being fed thereto, so that the water is filtered outwardly through the body. Floating and suspended solids left behind on the inner wall of the filter body are washed off. As they are carried upward by the rotation of the filter body, the solids are washed off by jets of water from the nozzles above the filter body. The solids are washed into the hopper, and then are discharged to the outside through the hollow shaft. The procedure is continuously repeated for the filtration of raw water. Since the filter body is under water for only about two-fifths of its height, as noted, the filtration area is limited and the washing requires the use of water under pressure. In actual filtration operations difficulties are involved in handling water that contains cyanophyta, coagulated floc, and biological floc. Moreover, the equipment is costly because of the expensive stainless steel screen employed as the filter.
The present invention has for an object the provision of a continuous rotary drum filtration apparatus capable of eliminating the foregoing problems of the last-mentioned filtration method. The construction of the apparatus is characterized in that horizontal bars, metal screen, or the like is extended between the peripheries of disc-shaped end plates to form a drum-shaped frame and a filter cloth of a water-permeable fabric with a long pile or flocked fabric is wrapped round the frame to form a hollow filter body. A rotating shaft connects the filter body with a discharge pipe and supports the filter body while it is submerged in a water conduit. A hopper is located immediately below the filter body in the conduit. The hopper carries on its upper parallel edges a pair of rolls in contact with the filter body.